Wear can be caused by the relative motion between two surfaces that are in close contact, causing deformation or removal of the material; this is known as mechanical wear. Wear can also be caused by other sources such as harsh or reactive chemicals, or cavitation.
Wear particle analysis is a good method for determining the type of wear, and the possible sources of wear particles e.g. gears, pulleys, bearings, etc.
Below, we examine the various types of wear that can occur in machines:
Abrasive WearAbrasive wear is caused by hard particles coming in contact with machine components during operation. Because these particle can be harder than the surfaces they come in contact with, they lead to damage and deformation.
The abrasive particles are usually as a result of dirt and contamination present in a machine. Proper filtration of lubricants and checking air vents and seals can help prevent these types of particles from entering the machine and causing wear.
Cutting WearThis type of wear typically occurs when a hard and abrasive particle becomes embedded in a softer material. As a machine is operating, normal system forces and interactions cause long and narrow strips be cut from the softer material. Cutting wear particles can be identified by their long aspect ratio (their length vs width), and this always indicates that there is abnormal wear occurring inside a machine.
Adhesive WearThis form of wear is usually caused by insufficient or improper lubrication in a system. Friction and cohesive forces can cause materials to become dislodged from the surface. In some instances, inadequate lubrication can also lead to air or gas entrainment between surfaces, and cavitation, which causes pitting and cracking of the surfaces. Using the appropriate viscosity lubricant can help prevent adhesive wear.
SlidingSliding wear occurs when a system is under stress due to do excessive loading or greater than normal operational speeds. This leads to heat build up that can degrade the lubricant and allow metal-on-metal contact; sliding between the surfaces leads to damage. This form of wear can also be caused by a stationary surface coming in contact with a moving component.
FatigueFatigue occurs when component surfaces begin to crack due to stressing. This may be caused by excessive loads on the surface. Heat build-up can also cause fatigue if the lubricant has degraded and cannot adequately function. Fatigue wear can cause material to break away from the surface, which could lead to wear damage in other locations of the machine.
CorrosionCorrosion can be caused by chemical reactions that remove material from the surface of components. Oxidation due to acidic conditions is one cause for this. Unexpected electrical currents can also lead to damage by welding or pitting the surfaces of parts and components. Other causes include the presence of water, or heat and combustion near materials.
Proper maintenance and machine monitoring can help prevent the types of wear listed above; at the very least, it allows you to notice any abnormal wear before there is significant damage to the machine.